The invention relates to a portable power tool having a housing with a rotation motor and a grease lubricated angle drive including a pinion and a bevel gear located in a gear chamber and coupling the output shaft to the motor.
This type of tool is commonly used as grinding machines, power wrenches, drilling machines etc. where a good accessibility in cramped working areas and/or a good torque reaction control have high priority. However, a problem concerned with this type of tool relates to a limited service life of the angle drive. This is mainly due to a poor lubrication of the gear teeth of the pinion and bevel gear. Several attempts have been made to cure this problem with more or less discouraging results.
Angle drives for the above mentioned applications are lubricated with grease, supplied at the assembly of the angle drive and/or added at certain operation intervals. What always happens during tool operation is that the grease in the angle drive gear chamber is thrown off the gear teeth and is deposited on the walls of the gear chamber. The result is that after a while no grease is left on the gear teeth and there will be a dry gear teeth engagement. This is detrimental to the service life of the angle drive.
One way of obtaining a satisfactory lubrication is to add a certain amount of grease to the gear chamber at short intervals, either manually via a grease nipple or automatically by a grease dispensing device originally filled with a larger amount of grease. Even a dispensing device has to be refilled at some intervals, though. When the gear chamber eventually after repeated supply has been filled up with grease to a certain extent the angle drive has to be dismantled for emptying and/or replacing the grease. Introducing extra service intervals just for ensuring a good angle drive lubrication is undesirable since it decrease the efficiency of the tool.
Another way of controlling grease application on the gear teeth is to accomplish relocation of the grease already present in the angle drive gear chamber from areas of deposition toward the gear teeth, continuously or at certain operation intervals.
Still another way of accomplishing an acceptable grease supply to the gear teeth would be to fill up the gear chamber with grease to a very large extent, which would avoid the need for repeated replenishing of grease for the angle drive lubrication. Instead, another problem would occur in that a great part of the grease volume would be in a continuous contact with the gear teeth and be agitated to high temperatures due to viscous friction. That would result in a destruction of the grease where lighter constituents would be separated from heavier constituents, and the lubricating effect of the grease would be severely impaired.
The main object of the invention is to provide a power tool with an angle drive in which extra service intervals are avoided in that the gear chamber is originally filled with grease to a large extent, and in which the grease is protected from being unnecessarily agitated to high temperature levels by the gear teeth.
Another object of the invention is to protect the grease in the gear chamber from a continuous gear teeth agitation by providing a screen device in a close vicinity to the bevel gear, thereby covering a substantial part of the bevel gear teeth and preventing a great part of the grease volume from getting into contact with and replenishing continuously the bevel gear teeth with grease. This avoids hot agitating of the grease.
Further objects and advantages of the invention will appear from the following specification and claims.